1. Field of the Invention
The present invention generally relates to an image forming apparatus such as a copier, a printer, a facsimile machine, or a multifunction machine including at least two of those functions.
2. Discussion of the Background Art
In general, in image forming apparatuses, such as copiers, printers, facsimile machines, or multifunction machines including at least two of those functions, etc., sheets of recording media on which images are formed are discharged by a pair of rollers, a driving roller and a driven roller, onto a discharge tray.
Recently, to make the image forming apparatuses more compact while improving usability thereof such as removability of output sheets from the discharge tray, several approaches, described below, have been advanced.
For example, in one known image forming apparatus, the driven roller serving as the discharge roller can rotate around a shaft of the driving roller serving as the other discharge roller. Thus, the position of a discharge nip where the driving roller and the driven roller contact is changed, so that the direction in which the sheet is discharged to the discharge tray (hereinafter “sheet discharge direction”) is vertically variable according to the size of the sheet enabling the sheet to be neatly stacked on the discharge tray.
Although the sheets can be stacked on the discharge tray neatly in this configuration, this configuration does not contribute to the removability of the output sheets from the discharge tray. Moreover, because only the driven roller can move, the angle at which the sheet enters the discharge nip changes significantly in practice, which can invite jamming of the sheet before and after the driven roller is moved. Thus, it is difficult to attain reliable discharge of sheets.
Therefore, in this configuration, in addition to the sheet discharge direction, it is necessary that the direction (angle) of the discharge tray be movable to stack the sheets neatly on the discharge tray. In addition, it is necessary to change the shape of a transport guide in conjunction with the change of the sheet discharge direction to improve sheet transport.
Moreover, in the configuration in which the sheet discharge direction is changed by changing the position of only the driven roller, discharge of sheets would be difficult when only the direction of the discharge nip is changed without changing a sheet transport path, that is, the angle at which the sheet initially contacts the discharge roller. In smaller image forming apparatus such as printers, because the sheet transport path is more curved, the output sheets are likely to curl, and the range of cardboard thicknesses that the image forming apparatuses can accommodate will decrease.
Another known image forming apparatus includes a sheet discharge space inside a housing thereof to reduce the area required to install the image forming apparatus. The image forming apparatus further includes a fixed lower tray disposed beneath a discharge port provided in the sheet discharge space and an movable upper tray disposed above the fixed lower tray. A downstream portion of the upper tray in the sheet discharge direction is supported by a shaft perpendicular to the sheet discharge direction so as to be vertically rotatable. The upper tray can be lowered until a space between its loading face and the discharge port is equal to a height of the sheets that the upper tray can accommodate. As the upper tray can be lifted until its bottom face is above the discharge port, the sheet can be discharged onto the lower tray through the identical discharge port.
Yet in another image forming apparatus, an additional tray can be attached thereto in addition to an existing discharge tray so that output sheets can be stacked on separate trays according to its operational modes, such as print mode and facsimile mode. The image forming apparatus further includes a switching guide to switch the sheet discharge direction between a direction leading to the existing tray and that leading to the additional tray, and a driving connector that drives a discharge member to discharge the sheet. When the additional tray is used, the driving connector causes the switch guide as well as the discharge member to discharge the sheet to the additional tray using a driving force of a transport member to transport the sheet to the existing tray.
However, increasing the number of discharge trays makes management of components more complicated. It might happen that the additional tray is missing when users desires to use it.
Herein, regarding usability, it is preferable that jammed sheets can be removed easily from the image forming apparatuses. For example, in typical tandem multicolor image forming apparatuses, a sheet transport path is disposed at a front side of the image forming apparatus so that jammed sheets can be removed from the front side.
Although such an arrangement has advantages it also has several drawbacks. For example, as the sheet discharge port is disposed on the front side, the sheet discharge port is an obstacle to the visibility and accessibility from the front side as well as from a lower side.
This problem may be solved by using a movable tray that can rotate to a substantially vertical position so that the output sheets can be kept substantially vertically. However, a subsequent sheet will be discharged at such an angle that its leading edge hits the sheets already stacked on the movable tray, which increase possibilities of damage to the stacked sheets and/or sheet jamming.
In view of the foregoing, there is a need to maintain a constant stress to a face on which the sheet is stacked so as to stack the sheets neatly thereon even when the sheet discharge direction is changed, which known image forming apparatuses fail to do.